Belini,
This is how I do it:
#include <GUIConstantsEx.au3>
#include <WindowsConstants.au3>
; Set resize mode for controls
Opt("GUIResizeMode", $GUI_DOCKAUTO)
Global $iGUIInitSize = 500
$hGUI = GUICreate("Test", $iGUIInitSize, 500, -1, -1, BitOR($WS_SIZEBOX, $WS_SYSMENU))
$cButton = GUICtrlCreateButton("Resizing text", 10, 10, 80, 30)
$iLast_Control = GUICtrlCreateDummy()
GUISetState()
GUIRegisterMsg($WM_SIZE, "_WM_SIZE")
While 1
Switch GUIGetMsg()
Case $GUI_EVENT_CLOSE
Exit
EndSwitch
WEnd
Func _WM_SIZE($hWnd, $iMsg, $wParam, $lParam)
#forceref $iMsg, $wParam, $lParam
If $hWnd = $hGUI Then
; Calculate required font size
Local $aGUI_Size = WinGetClientSize($hGUI)
$iFontSize = Int(2 * (.25 + (8 * $aGUI_Size[0] / $iGUIInitSize))) / 2
; Reset font size for all controls on main GUI
For $i = 0 To $iLast_Control
GUICtrlSetFont($i, $iFontSize)
Next
EndIf
EndFunc ;==>_WM_SIZE
M23